Air Traffic Surveillance – How can a Boeing 777 vanish without a trace?

Nearly two weeks ago, a Boeing B777-200 of the Malaysian flag carrier Malaysia Airlines vanished with no trace. Flight MH370, the regular daily flight between Kuala Lumpur and Beijing, carried 239 persons on board and was under the command of a highly experienced crew. The flight never reached its destination, and an unprecedented search for the overdue aircraft was launched. Initially the search concentrated on an area in the South China Sea where the last position was received. However, the search area was progressively enhanced covering the Bay of Bengal, large parts of the Indian Ocean, and several territories over China and Central Asia. NASA was involved to scan the earth surface analyzing every object over 30 meters, and even the public at large is invited to analyze satellite data on the internet.

Was the aircraft victim of an accident or was its disappearance a result of terrorism? Was it shot down, hijacked by intruders or the crew, did it ditch and sink rapidly as a consequence, or did it land successfully at one of the 634 runways on its theoretical pathways suitable for a B777 to be stowed away and held for ransom? We might not know the answer to these disturbing questions for months and years to come. However, the travelling public is astonished to learn that the B777 of flight MH370 was not under active surveillance. How can it be that in times where anybody can be located homing on a cell phone a commercial airliner just gets lost?

Since the end of World War II, air traffic has been surveyed by radar. Primary radars pick up the reflection of an electronic beam from an aircraft to determine its position. This technology has its limitations given a range of only 70 nautical miles. Aircraft have therefore been equipped with transponders that respond to radar inquiry. These secondary radar systems typically range up to 250 nautical miles. If an aircraft flies outside of the range of a radar station, such as over the open sea or remote areas, so called procedural air traffic control, which involves position reports and estimates, is used to control air traffic. Nevertheless, unknown to the travelling public, most of the commercial air traffic is not under active control for a large amount of a given flight.

The industry has developed the Aircraft Communication Addressing and Reporting System (ACARS), on which operators can transmit via satellite aircraft data from anywhere in the world on a privately operated network. Typically, only engine data are regularly sent for analysis during a flight to a carrier’s base and to the engine manufacturer, and some company communications (text messages) are done. However, given that this private sector communication solution is expensive, airlines limit the usage of these services and don’t send other data, such as position reports, over these networks.

Over 10 years ago, a new technology called Automatic Dependent Surveillance – Broadcast (ADS-B) has been developed in the United States. With ADS-B, each aircraft will be equipped with a digital transmitter reporting its position and other parameters every second to a simple ground based receiver. The new system costs less than 10 percent of traditional radar systems, and it allows following any aircraft continuously. Trials in Alaska have been so successful that the American Federal Aviation Administration (FAA) has made the system mandatory on all aircraft in the United States by 2020. Today, about 60 percent of commercial airlines are equipped with ADS-B, but only a few countries (e.g. USA, Australia) have ground installations to receive the signals. To address the lack of surveillance over remote areas where no ground installations are possible, private operators are currently developing satellite systems that could pick-up and rebroadcast ADS-B at reasonable cost. Would flight MH370 have been equipped with ADS-B, the search would have been a question of hours, as the reference point would have been the point of its last transmission seconds before disappearance.

Schematic of ADS-B Systems

The Bank is currently implementing the Pacific Aviation Investment Program (PAIP). Several PAIP countries are receiving ADS-B systems, equiping both aircraft and ground stations, to implement air traffic surveillance at a fraction of the cost of radar in these developing aviation markets. Despite the fact that the system is not yet satellite based, it already greatly improves safety as most regional flights never leave the range of the ground stations. This approach allows emerging countries to leapfrog constraints related to mainstream transportation technology by using modern ICT technology.

Aircraft operating between the Pacific Islands, like this Britton Norman, will be equipped with ADS-B allowing constant surveillance

Comments

I was also under the impression that an aircraft was constantly monitored and that's why I was wondering how come they didn't find the Malaysian airline yet. The same exact thing happened to the Air France Flight 447.

Thanks for the informative post. I hope they find a solution to avoid these strategies

Hello Charles - Your comments are bang on, ADS-B used by ATC would eliminate much of the cost of this search, provided the system couldn't be easily disabled. Also, don't you think it is time to replace black boxes with data streaming? No reason why data couldn't be streamed, bandwidth is small compared to entertainment and onboard wifi systems and this would give more info than ADS-B on aircraft problems to help prevent further accidents. Cheers, Glen

Hi Glen,
I agree that data streaming for the so called "black box" should be done via satellite link. Typically, a data recorder catches about 4000 operational data every second. These data could be sent every, say every minute, via satellite link taking very little bandwith. I am sue that the AF447 and MH370 accident will accelerate the discussion on this feature. However, the agreement for this must involve a majority of countries. The best platform is ICAO.

Very well explained--as far as it goes. But you must add the difference between ADS-B/IN and /OUT. Not only will this tell the reader that in the context in which you are writing--the missing 777--what data ADS-B makes available is very different in its usefullness. Also, there is no "business case" for /OUT for any airline such as Malaysian but there is a powerful one for /IN. However, the FAA is only funding the ground stations for /OUT which is one of worst public (FAA) decisions ever (for which no FAA executive has ever paid any price).

Well, let me correct you by going into some details. There are two ADS-B systems: the classical one with transponders extending their squawk on 1090 MHz, and the UAT system, which works on 978 MHz. The latter allows ADS-B IN (weather, traffic, data messages) and OUT (position report). However, UAT is only suitable for General Aviation and aircraft flying below FL180 (regulation starting 2020 in the US).

Typically, all new airliner and commercial aircraft since 2006 are equipped with a mode S transponder, including an extended squitter. That means that today 60 percent of all carriers are in fact transmitting ADS-B, but there are just a few ground stations (and so far no space based systems), that can read the signals. These airliners do not need ADS-B in, because they get all the data by other systems, such as TCAS (traffic) or ACARS (company communication, weather etc.). Therefore, ADS-B OUT on 1090 ES is sufficient.

Finally, I disagree with your statement that the US is only funding ADS-B OUT. In fact, the US is the ONLY country in the world that installs nationwide (nearly completed) a ground based dual ADS-B (1090 ES / UAT) system. That means that all aircraft equipped with a UAT (including my little Cessna) are receiving ADS-B IN free of charge.

I am wondering as you are, how can an aeroplane this size fly for some time undetected by any air defense radars or any satellite..!! As they say you can be located if your smart phone is ON, but unfortunately we can not locate a 777 plane with devices on board designed for this purpose...
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Thank you Dr. Charles,
Nader

Hi Charles - Thank you for these comments. Just one additional thought: It would have been possible for the crew to disable the ADS-B transmitter the same way they (possibly) switched off the transponder. Let's hope they find some evidence. Cheers. Norbert

Yes, ABS-B on a 1090 extended squitter can be turned off by the crew, by switching off the transponder. Only ADS-B that is transmitting on a UAT (978 MHz) typically is ON as long as the Battery Switch of an aircraft is ON.

I think that in the future aircraft systems will be redesigned so that an ADS-B system never can be switched off. However, we don't know why the transponder stopped functioning. It could have been turned off manually, flown out of range, or malfunctioned maybe due to an electrical fire.